1.
You use ~ to introduce a point which is not directly relevant to what you are saying, often a question or extra information that you have just thought of.
‘I didn’t ask you to come. Incidentally, why have you come?’
ADV: ADV with cl
2.
If something occurs only ~, it is less important than another thing or is not a major part of it.
The letter mentioned my great-aunt and uncle only ~.
ADV: ADV with v