'Sue' is Latin for 'to follow' — from 'sequi.' Legal pursuit: following someone through the courts.
To institute legal proceedings against a person or institution; (archaic) to make a petition or appeal.
From Anglo-Norman 'suer' and Old French 'sivre' (to follow, to pursue, to accompany), from Vulgar Latin *sequere, from Latin 'sequī' (to follow, to accompany, to pursue as a consequence), from PIE *sekw- (to follow). The PIE root *sekw- is exceptionally productive: it generated Latin 'sequī' (follow), 'sequentia' (sequence), 'secundus' (following, second), 'sect' (a following, a group that follows a leader), 'consecutive,' 'ensue,' and 'execute' (to follow through to completion). Through Greek 'hepesthai' (to follow) it connects to 'acolyte.' To sue someone is etymologically to follow them — to pursue a person
The words 'sue,' 'suit,' 'suite,' and 'suitor' are all from the same root — French forms of Latin 'sequī.' A 'suit' was originally a following or pursuit (a suit at law, a suit of clothes that follows/matches). A 'suite' is a set that follows together (hotel rooms, musical movements). A 'suitor' is one