어쩐지 + reason: 어쩐지 …더라고요 · 어쩐지 기분이 이상해요 (somehow)
no wonder; somehow
Example
오늘 휴일이었어요? 어쩐지 길이 한산하더라고요.
Was today a holiday? No wonder the streets were so quiet.
Word parts
From 어찌하다 'how' + -ㄴ지 'whether': 'I didn't know how, but …'.
Good to know
Two uses: after you learn the reason, 어쩐지! means 'No wonder!'; for an unexplained feeling it means 'somehow', like 왠지.