Elusive
WordNet
adjective
(1) Skillful at eluding capture
"A cabal of conspirators, each more elusive than the archterrorist"- David Kline
(2) Difficult to describe
"A haunting elusive odor"
(3) Be difficult to detect or grasp by the mind
"His whole attitude had undergone a subtle change"
"A subtle difference"
"That elusive thing the soul"
WiktionaryText
Adjective
elusive
- evading capture, comprehension or remembrance
- elusive criminal arrested
- rarely seen
- difficult to describe
- A precise definition of diarrhea is elusive (Robbin's pathology, 8th ed)