Realistic (4-6)
'realistic' is the definition.
(similar in meaning)
This is all the clue.
(Other definitions for lifelike that I've seen before include "Exactly like real person or thing" , "True-to-life" , "Realistic" , "Could be mistaken for the real thing, like figure in wax museum" , "Resembling a real person or thing" .)
(Other definitions for hard-headed that I've seen before include "as aggressive old goats might be?" , "Tough" .)