Few ancient groups have suffered more severely at the hands of language than the Pharisees. A movement of Jewish laypeople devoted to the application of Torah to everyday life, who produced traditions that became foundational to rabbinic Judaism and survive to this day, they are remembered in English primarily as a byword for hollow religious pretension. The word 'pharisaical' carries no positive connotations whatsoever; to call someone a Pharisee is an insult.
The historical Pharisees were a significant force in Second Temple Judaism, probably the most influential religious movement among common Jewish people in the first century CE. They extended the concept of priestly holiness to everyday life, developed oral traditions (the 'tradition of the elders' mentioned in the Gospels) to apply biblical law to new situations, and emphasized study, prayer, and ethical behavior. Many of the religious practices most recognizable in contemporary Judaism - the form of synagogue worship, the structure of prayer, the centrality of Torah study - derive from Pharisaic foundations. The Talmud, which forms the core of rabbinic Judaism, is essentially the legacy of the Pharisaic movement.
Jesus's conflicts with the Pharisees, reported extensively in the Gospels, focused primarily on specific disagreements about the application of Torah rather than on Pharisaism as a whole movement. The Gospels record Jesus dining with Pharisees, being warned by friendly Pharisees about threats to his life (Luke 13:31), and acknowledging the validity of Pharisaic teaching even while criticizing Pharisaic practice ('do as they say, not as they do,' Matthew 23:3). Paul identified himself as a Pharisee (Philippians 3:5, Acts 23:6) and did not treat the designation as shameful.
Matthew 23, however - a sustained denunciation of scribes and Pharisees as hypocrites, blind guides, whitewashed tombs, and a brood of vipers - dominated Christian reception of the Pharisees. The word 'hypocrite' in this chapter is applied to Pharisees so repeatedly that it became almost definitionally their characteristic failing. In the centuries following the destruction of the Temple (70 CE), when Christianity and rabbinic Judaism were developing as rival interpretive traditions, Matthew 23 became a source for anti-Jewish polemic that significantly distorted historical understanding.
In English, 'pharisaical' means: outwardly observant of religious rules while inwardly corrupt or indifferent to their spirit; self-righteous in a way that prioritizes performance over genuine virtue; ostentatiously religious in ways designed to impress rather than to be. The adjective is used in religious, political, and personal contexts to describe the gap between claimed principle and actual practice - the performance of virtue as a substitute for virtue itself.
The word's durability lies in the accuracy with which it names a genuine human tendency - the tendency to use the forms of morality as a substitute for its substance, to use religious or ethical performance as social currency rather than as genuine expression. That this tendency is named after the Pharisees is historically unjust; it is no more characteristic of the historical Pharisees than of any other religious community. But the word has become, through the centuries, the permanent English name for a universal phenomenon.