A treiglad meddal is applied after a number of prepositions:
‘am’ (at / for): Aethon ni am dro i'r traeth.
We went for a walk to the beach. (tro)
‘ar’ (on): Gwnaethon nhw gwrdd ar drên.
They met on a train. (trên)
‘at’ (to / at): Dylai hi fynd at feddyg.
She should go to a doctor. (meddyg)
'dros’ (over): Mae niwl dros fynydd.
There is mist over a mountain. (mynydd)
‘trwy’ (through): Mae'r llwybr yn mynd trwy goedwig.
The path goes through a wood. (coedwig)
‘dan’ (under): Roedd y cae dan ddŵr yn y llifogydd.
The field was under water in the flood. (dŵr)
'wrth’ (by): Mae'r siop wrth lyfrgell.
The shop is by a library. (llyfrgell)
‘o’ (from): Teithiodd o Gaerdydd.
He travelled from Cardiff (Caerdydd)
‘i’ (to): Mae'r amser yn chwarter i bedwar.
The time is quarter to four. (pedwar)
‘heb’ (without): Peidiwch â mynd trwy'r dydd heb fwyd.
Don't go all day without food. (bwyd)
‘tan’ (until): Gadewch y gwaith tan ddydd Llun.
Leave the work until Monday. (dydd)
‘gan’ (by / from): Mae'r llun gan fyfyriwr yn y coleg.
The picture is by a student in the college. (myfyriwr)
A treiglad meddal is applied after the personal possessive pronouns ‘dy’ (‘your’) and ‘ei’ (‘his’):
Dy ddewis di yw prynu ei gar ai peidio.
It is your choice whether or not to buy his car. (dewis, car)
Roedd ei fab yn siarad â dy frawd.
His son was speaking to your brother. (mab, brawd)
A treiglad meddal is applied after adjectives and nouns following the linking word ‘yn’ (traethiadol).
Cerddon ni o amgylch y ganolfan siopa yn gyflym.
We walked around the shopping centre quickly. (cyflym)
Mae bron pawb yn y teulu yn feddyg.
Almost everyone in the family is a doctor. (meddyg)
However, a treiglad in not applied in the case of ‘ll’ and ‘rh’:
Mae hwn yn llyfrgell ac mae'n rhad ac am ddim i fenthyg llyfrau.
This is a library and it is free to borrow books.
A treiglad is not applied to a verb noun following ‘yn’ (traethiadol):
Roedd y plant yn dringo ac yn gweiddi yn y maes chwarae.
The children were climbing and shouting in the playground.
A treiglad meddal is applied after dyma ('here is...'), dyna ('there is..') and dacw ('over there is...') :
Dyma westy a dacw fwyty.
Here is a hotel and over there is a restaurant. (gwesty, bwyty)
A treiglad meddal is applied after the conjunction ‘neu’ (or):
Ydy'n well gyda chi fyw mewn pentref neu dref?
Do you prefer to live in a village or a town? (tref)