Premonish \pri-MON-ish\ , verb;
1. To warn beforehand
This word dates to the 1500's and comes from Latin praemonere ("to forewarn, foretell"), which is a combination of prae- + monere ("pre-" + "to advise, warn").
Premonish made me think of admonish, which is first attested in 1340. It comes from Old French amonester ("urge, encourage, warn"), which derives from Vulgar Latin *admonestare from Latin admonere ("bring to mind, remind, suggest" and "warn, advise, urge"). It's a combination of ad- + monere ("to" + "advise, warn"). Notice that there is no -d- in the Old French word. Originally the Old English word was -d-less as well, but around 1500 it reappeared thanks to influence from the Latin form.
There's another related word in English: monish.
Monish is first attested in 1382 and means "to warn." It's either another form of admonish with a weakened prefix, or it came from Anglo-Norman and Old French monester, which is most likely a derivative of Latin monere. This word is now rare and reserved for literary and archaic uses.
Today's word and the first definition were both taken from Dictionary.com's 'Word of the Day' for Friday, May 6
Etymologies come from the Oxford English Dictionary and/or Etymonline.com