siec
seicThese are both obviously borrowings of English
cheque. The amusing transposition of vowels stems from the quirks of their respective orthographies: <i> is the only vowel which indicates palatalisation of <s> in Welsh so it needs to be inserted here before <e>. Both <e> and <i> are palatal vowels in Irish ("slender" or "
caol" in native terminology) but for some reason <e> alone isn't sufficient to indicate a following consonant is palatalised in Modern Irish so an <i> needs to be inserted after it.
What I find particularly confusing, however, are the gender assignments. Masculine is the unmarked gender in Welsh so I would expect
siec to be masculine. It isn't, though, it's feminine and I have no idea why. Meanwhile, I would expect
seic to be feminine since almost all words ending in a slender consonant in Irish are, but it's not, it's masculine!
"Richmond is a real scholar; Owen just learns languages because he can't bear not to know what other people are saying."--Margaret Lattimore on her two sons