ProPOSEL is a prototype prosody and PoS (part-of-speech) English lexicon for Language Engineering, derived from the following language resources: the computer-usable dictionary CUVPlus, the CELEX-2 database, the Carnegie-Mellon Pronouncing Dictionary, and the BNC, LOB and Penn Treebank PoS-tagged corpora. The lexicon is designed for the target application of prosodic phrase break prediction but is also relevant to other machine learning and language engineering tasks. It supplements the existing record structure for wordform entries in CUVPlus with syntactic annotations from rival PoS-tagging schemes, mapped to fields for default closed and open-class word categories and for lexical stress patterns representing the rhythmic structure of wordforms and interpreted as potential new text-based features for automatic phrase break classifiers. The current version of the lexicon comes as a textfile of 104052 separate entries and is intended for distribution with the Natural Language ToolKit; it is therefore accompanied by supporting Python software for manipulating the data so that it can be used for Natural Language Processing (NLP) and corpus-based research in speech synthesis and speech recognition. 1. ProPOSEL: Derivation and Rationale A pronunciation lexicon is an integral part of the front-end NLP module in a generic Text-to-Speech (TTS) synthesis system and constitutes a natural way of giving such a system both prosodic and syntactic insights into input text. For English, three such resources- originally developed for Automatic Speech Recognition (ASR) and listing words and their phonetic transcriptions- are widely used: CELEX-2 (Baayen et al, 1996); PRONLEX (Kingsbury et