Boyd’s Bible Dictionary:

(set apart). A Jewish seat, strictly orthodox in religion, and politically opposed to foreign supremacy (Matt. 23:23-33; Luke 18:9-14).

Concise Bible Dictionary:

This name was given to a religious school among the Jews; it is supposed to have been derived from the Hebrew word parash, signifying “to separate”; it was given to them by others, their chosen name being chasidim, “pious ones.” Josephus speaks of them as early as the reign of Jonathan (B.C. 161-144). They prided themselves on their superior sanctity of life, devotion to God, and their study of the law. The Pharisee in the parable thanked God that he was “not as other men” (Luke 18:11). Paul, when before Agrippa, spoke of them as “the most straitest sect.” The Pharisees included all classes of men, rich and poor: they were numerous, and at times had great influence. In the council before which Paul was arraigned they were well represented (Acts 23:6-9). They were the great advocates of tradition, and were punctilious in paying tithes. In many respects the ritualists of modern days resemble them.
The Lord severely rebuked all their pretensions, and laid bare their wickedness as well as their hypocrisy. It may have been that because of the great laxity of the Jews generally, some at first devoutly sought for greater sanctity. Others, not sincere, may have joined themselves to the sect, and it thus degenerated from its original design, until its moral state became such as was exposed and denounced by the Lord. The very name has become a synonym for bigotry and formalism. Probably such men as Gamaliel, Nicodemus, and Saul were men of a different stamp, though all needed the regenerating power of grace to give them what they professed to seek.

Strong’s Dictionary of Greek Words:

of Hebrew origin (compare 6567); a separatist, i.e. exclusively religious; a Pharisean, i.e. Jewish sectary
KJV Usage:

Jackson’s Dictionary of Scripture Proper Names:

the separated: expounders

Potts’ Bible Proper Names:

Separated; a separatist; self-righteousness:―a Jewish sect, Matt. 3:7. {Separati}

From Manners and Customs of the Bible:

Matthew 22:15. Then went the Pharisees, and took counsel how they might entangle him in his talk.
The Pharisees were a politico-religious party among the Jews. Their origin is involved in obscurity, but it is commonly supposed that the beginning of the party dates from a time shortly after the Babylonish Captivity. A Pharisee is, literally, one who is separated; and it is thought that the name was given because these people separated themselves from all Levitical impurity. They were doubtless a pure people in the beginning, their design being to preserve the law from violation, and the Jewish people from contamination. As their influence increased, and political power came into their hands, they lost much of their original simplicity. In the time of Christ they were very numerous and influential, and occupied the chief offices among the Jews. They were divided into two schools: the School of Hillel, and the School of Shammai.
The Pharisees were especially distinguished for belief in an Oral Law of Moses, as well as a Written Law. This Oral Law was supposed to be supplementary to the Written Law, and, with various comments added from time to time, had been handed down by tradition. The Pharisees had great veneration for this traditionary code, and for the traditionary interpretations. They placed them in authority on a level with the Written Law, and even above it. See note on Matthew 15:3 (#672). As a body, they were not chargeable With immorality in life; on the contrary, there were many zealous and conscientious men among them, and many things which they taught were worthy of being observed, as Jesus himself admitted. See Matthew 23:3. These teachings were from the law; it was when they attempted to make their traditions valid that Jesus denounced them. The great error of the most of them consisted in substituting human tradition for divine law, and in observing mere external forms, many of them of a most wearisome as well as puerile character, instead of seeking for inward purity of heart, which would have been accompanied by corresponding blamelessness in life.
It was but natural that such teachers should be bitterly opposed to Christ, and that he should vehemently denounce them and warn the people against them. They endeavored in various ways to “entangle him in his talk,” (literally, to ensnare or entrap him,) and in every possible manner they exhibited their hatred. His stinging rebukes tingled in their ears and rankled in their hearts, and made them threaten his life.