A root in The Etymologies of the 1930s glossed “swallow” with variant ᴹ√LANK and derivatives ᴹQ. lanko/N. lhanc “throat” (Ety/LAK¹, LANK), the latter an element in N. tarlanc “stiff-necked, obstinate” (Ety/TÁRAG). This last word was changed to S. tarlang in Tolkien’s later writings (PE17/92; RC/536), consistent with an earlier but rejected form ᴹ√LANG for ᴹ√LANK in The Etymologies (Ety/LANK).
In later writings, Q. lango/S. lang meant “neck” rather than “throat”, so it is tempting to retain ᴹ√LAK for “throat” and other swallow-words. But it would be very confusing to have such similar but unrelated words for “neck” and “throat”, so I recommend using the root ᴹ√SLUK for “swallow” instead, and Q. lango, S. lang for both “neck” and “throat”.