sloganeer v.

1670s, earlier slogorne (1510s, Gavin Douglas), "battle cry," from Gaelic sluagh-ghairm "battle cry used by Scottish Highland or Irish clans," from sluagh "army, host, slew," from Celtic and Balto-Slavic *slough- "help, service." Second element is gairm "a cry" (see garrulous). The metaphoric sense of "distinctive word or phrase used by a political or other group" is attested from 1704 (as slughon). The spellings also included a fully folk-etymologized slughorn.

noun word-forming element meaning "one who" (operates, produces, deals in); Englished form of French -ier, from Latin -arius, -iarius; compare -ary. Usually in English words of more recent borrowing from French; older words tend to keep -ier.