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os

if

ConjunctionA1

"os" means "if" in Welsh (conjunction). Mutation forms: Treiglad Llaes → hos.

Mutation forms

In Welsh, the first letter of "os" changes depending on the grammatical context. These are the mutated forms:

MutationForm
Base formos
Treiglad Llaeshos

"os" in context

Os wyt ti eisiau rhedeg, yna rheda.

If you want to run, then run.

A1

Dim problem, wrth cwrs, os chi'n mynd

Of course it's not a problem if you go.

A2

"A beth ydych chi'n yfed?" "Cwrw, os oes gen i, neu ddŵr os nad oes gen i gwrw." "'Tydych chi ddim yn yfed gwin?"

"And what do you drink?" "Ale if I have it, or water if I don't have ale." "Don't you drink wine?"

C1

Wyt ti'n gallu siarad yn arafach, os gwelwch yn dda?

Could you please speak more slowly?

B1

Os na fydd gennych chi docyn dilys, gallwch gael eich erlyn a chael dirwy o hyd at £1000.

Failure to have a valid ticket may result in prosecution and a fine of up to £1000.

B2

Further reading

Welsh Mutations Explained — Soft, Nasal & Aspirate →Welsh Pronunciation — It's Actually Easier Than English →How to Learn Welsh as an Adult — A Step-by-Step Roadmap →Best Apps to Learn Welsh (2026) →Browse all Welsh vocabulary →

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Related Welsh words

ond

but

neu

or

achos

because

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