WordNet sense 1 (difficult to deal with):

contrarious

WordNet sense 2 (tenaciously unwilling or marked by tenacious unwillingness to yield):

obstinate, stubborn, unregenerate

WordNet sense 3 (of timber; having fibers running irregularly rather than in parallel):

curly-grained, wavy-grained

WordNet sense 4 (not even or uniform as e.g. in shape or texture):

uneven