L2 vocabulary is commonly conceptualized in terms of a size or depth of one's total lexical knowledge and tested discretely with selection-type items. Concerns exist, however, regarding L2 users' ability to cope with unknown vocabulary, especially in the context of academic reading. This motivated the creation of a test which measures the ability to identify definitions for unknown terms in an academic text. The test comprised a 768-word introductory biology textbook excerpt with non-words replacing ten technical terms, and test takers were asked to write definitions for each term. The test was piloted with 158 prospective university students of varying L2 English proficiency. Support for test score interpretations was sought by investigating the test's reliability, correlation with reading comprehension, and the qualities of test-taker responses. Internal consistency was adequately high, and a moderate correlation with reading comprehension was found. Test-taker responses aligned with expectations, demonstrating utilization of the in-text definitions. The test shows promise for those interested in academic reading abilities and vocabulary learning.