Complex problem and Head ache

Head ache and complex problem are semantically related In some cases you can replace phrase "Head ache" with "Complex problem", this phrases are similar.

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

Complex problem and head ache are semantically related in complicated situation topic. Sometimes you can use "Complex problem" instead a noun phrase "Head ache".