The dictionaries I could find did not agree on whether the perfective form of the (imperfective) verb курить is either: (i) закурить or (ii) покурить.
What is the correct perfective partner for курить? Is it закурить, покурить, or neither?
I suspect that the answer might, in some sense, be neither, because both закурить and покурить have "imperfectivizations", закуривать and покуривать, respectively, both of which are hyponyms of курить. (Definition of hyponym, a word which I learned today -- по-русски.)
Thus one might expect that both закурить and покурить would be hyponyms of a "perfective partner of курить" if such a verb actually existed (it seems not to).
In particular, perfective verbs formed by adding the prefix по- sometimes are restricted to the specific meaning of "a little, for a while", while perfective verbs formed by adding the prefix за- sometimes are restricted to the specific meaning of "to begin to". This appears to be the case for покуривать/покурить and закуривать/закурить.
Although I should add as a caveat that I am assuming that покуривать does correspond in meaning to покурить, even though Wiktionary does not say this explicitly (it does say explicitly that the corresponding statement is true for закуривать and закурить).
Also since покуривать is apparently colloquial, I may be misleading myself by considering it too much. (I.e. maybe по- is just a perfectivizing prefix with no specialization in meaning for курить (definition 1), and those who use the colloquial term покуривать misunderstand (definition 3) the use of the по- prefix for курить, which maybe also explains why покуривать has not become a formally accepted word.) Wiktionary does say that покуривать has no perfective partner (1)(2).
Note: Here is a related previous question of mine. For смеяться, the по- and за- perfectivizing prefixes seem to have the same meaning as for курить, yet nevertheless посмеиваться and засмеиваться do not correspond in meaning to посмеяться and засмеяться according to one of the answerers.