Translucent is a nice word. It always makes me slightly hungry as it reminds me of ‘suculent’ and is most commonly encountered in cookery books referring to fried onions. I do like fried onions.

If something is translucent it allows light to pass through diffusely – just as partialy cooked onions probably do (I’ve never actually fished one out the pan to test that). It’s also described as semi-transparent.