لكم لكن للب
لُكْنَةٌ An impotence, or impediment, or a difficulty, in speech or utterance; (Mṣb;) a barbarousness, or viciousness, and an impotence, or impediment, in speech: (Ṣ:) or the not speaking Arabic rightly, by reason of a barbarousness, or viciousness, in the tongue: (Ḳ:) or the interposing of [words of] a foreign language in one's speech. (Mbr, TA.) See تَهْتَهَةٌ; and عُجْمَةٌ, with which it is syn.
لٰكِنْ, with the ن quiescent, has no government.
It means But after a negative proposition: but not after an affirmative: see إِلَّا.