To underdevelop means to develop something less than fully, leaving it incomplete or not as good as it could be. A photographer who underdevelops film in the darkroom doesn't leave it in the chemical bath long enough, resulting in pale, unclear images. A writer who underdevelops a character in a story gives readers only a vague sketch instead of a person who feels real and interesting.

The word appears most often in its past tense form, underdeveloped. An underdeveloped argument in a debate lacks the evidence and explanation needed to convince anyone. An underdeveloped country has less infrastructure, technology, and economic resources than it needs to support its population well (though many prefer terms like “developing country” instead). An underdeveloped skill is one you haven't practiced enough yet to use confidently.

When something is underdeveloped, the foundation might be there, but the work stopped too soon. A student who writes a promising first paragraph but then rushes through the rest produces an underdeveloped essay. The potential exists, but it needs more time, attention, or resources to reach its full form. Recognizing when something is underdeveloped is valuable because it shows you what needs more work, whether that's a science fair project, a friendship, or your backhand in tennis.