I'm wondering what the か in か弱い, か細い and similar words is. It seems to act as an intensifier. The Daijisen tells me simply that this か is a 接頭語, and translates it as いかにも; it doesn't seem to have its own entry or any further explanation. Speculations online seem to include:
- it is a corruption of 小【こ】, and so is a simple intensifier
- it implies "obviously 弱い・細い by sight"
My question: what does this prefix mean, and where does it come from? (For bonus points: can anyone give me some more examples, and is this prefix still productive?)