Numerous studies suggest that bilinguals demonstrate smaller vocabularies than monolinguals, and that bilinguals' breadth of vocabulary knowledge - both expressive and receptive - is linked to input frequencies in each language [e.g. Hoff, E., S. Welsh, S. Place, and K. Ribot. 2014. "Properties of Dual Language Input That Shape Bilingual Development and Properties of Environments That Shape Dual Language Input." In "Input and Experience in Bilingual Development", edited by T. Grüter, and J. Paradis, Vol. 13, 119-140. Amserdam: John Benjamins]. However, relatively little is known about the quality of bilinguals' knowledge of the words they do know (e.g. their understanding of how words relate to each other semantically) and how input frequencies influence that knowledge. Using the Cognitive Abilities Tasks - 4 (CAT-4), this study explored the potential links between three types of input sources - home language exposure, self-reported rates of language use in general, and language use with friends - and bilinguals' performance on two types of vocabulary tests in both Welsh and English: verbal analogy and verbal categorisation. Results revealed similar performance across-the-board in relation to their knowledge of English vocabulary, regardless of their exposure to and use of Welsh and/or English in general and with friends, but their knowledge of the links between words in Welsh was related to home language exposure and rates of language use. The implications and application of these results in practice are discussed.