The adjectives least, less, more, and most present difficulties for writers when the words are paired with other adjectives: Should hyphens be employed? And what about when little, much, and similar terms are involved?
Generally, do not hyphenate such constructions. The following examples are all correct:
“She bought the least expensive shampoo.”
“I’ve never heard a less interesting story.”
“That wasn’t the most regrettable part.”
“We have a more likely explanation.”
But use these words cautiously in such sentences. For example, “He made several more successful efforts” is ambiguous: Does it mean that the person added a few successful efforts to his record of previous successful ones, or that the person’s efforts were more successful than previous ones? Some writers choose to hyphenate “more successful” when appropriate in such a context, but such a strategy leads to inconsistency when the hyphen is omitted in a similar but unambiguous statement. “He made several additional successful efforts” or “He made several efforts that were more successful,” respectively, clarifies the writer’s intent without making exceptions.
Very is another problematic term. Most writers likely consider it obvious that no hyphen belongs in “John held up a very full bucket,” but very stands alone even when it modifies a hyphenated phrasal adjective, as in “They chose three very well-liked students.”
But compare these conventions with the custom for such words as little, much, seldom, and often. These words, all of which except often can be adjectives or adverbs, serve the latter function when they precede an adjective and a noun — and in this case, they require a hyphen. (That’s counterintuitive, because adjectives are often hyphenated to a following word, while adverbs rarely are.)
Here are some examples:
“Mary spoke about a little-understood aspect of the animal’s behavior.”
“He explained a much-misunderstood phenomenon.”
“The seldom-seen plant is found in only one place.”
“The project was plagued by interventions with often-inconclusive results.”
(As with phrasal adjectives, these word pairs are not hyphenated after the noun. For example, “Mary spoke about an aspect of the animal’s behavior that is little understood.”)
Note this exception: “The somewhat subjective report omitted some important details.”