Fucking

google

ref

early 16th century: of Germanic origin (compare Swedish dialect focka and Dutch dialect fokkelen ); possibly from an Indo-European root meaning ‘strike’, shared by Latin pugnus ‘fist’.

wiktionary

ref

From fuck +‎ -ing.

etymonline

ref

fucking (adj.)

present-participle adjective from fuck (v.). As a mere intensive, attested from 1893, probably older.