Gadfly and Head ache

Gadfly noun - One who is obnoxiously annoying.

Head ache and gadfly are semantically related In some cases you can replace phrase "Head ache" with "Gadfly", this terms are similar.

Head ache noun - Pain in the head caused by dilation of cerebral arteries or muscle contractions or a reaction to drugs.

Gadfly and head ache are semantically related in annoyance topic. Sometimes you can use "Gadfly" instead a noun phrase "Head ache".