I've been wondering about this for a while! I believe that d'ól is the past tense of ól (to drink), but what does the d' mean? This also seems to be the same for d'fhág, the past tense of fág (to leave).
Can anyone shed some light on this? Also, feel free to correct me if I am wrong on any of the above:)
It means "do", shortened as two "o"s are together. Past tense.
It used to be a feature of Irish that the past tense was always formed using do - do chaith sé (he threw); do thainigh mé (I came); etc. Before a vowel or a lenited 'f', which is silent, do became d' - d'oscail sí (she opened); d'fhág sé (he left).
Over time, do started to disappear in some variants of Irish, but it clung on in Munster Irish. When Irish was standardised, do was dropped, except before a vowel or a lenited 'f'. But a lot of speakers, particularly from the south, still use it, and you will hear it in the wild. And if you use it yourself no-one will correct you; it's not standard, but it's an acceptable variation.
Thanks for ye're replies.
Now that I know the answer is seems very obvious, but I couldn't find this explained anywhere online or in any of the Irish learning books I have!