||Sexual intercourse, to have sexual intercourse.
||I had a great flah last night.
I enjoyed intercourse last night.
||Possibly Irish 'Fleadh' - party
Note 'Fele' (Fíal) - that which causes shame, nakedness, pudenda.
Note 'Fell Óg' - a false virgin. (Joynt and Knott)
Possibly corruption of Old Irish 'Sleith' - act of surprising a sleeping woman, having intercourse with her. (Quin)
English 'Flay' - to criticise, to plunder (a person).
Old English 'Fléan', Middle Dutch 'Vlae', Old Norse 'Flá', from Germanic 'Flahan'. (Compact English Dictionary)