Practical English Usage is not a complete guide to the English language. As the title suggests, its purpose is practical: to give learners and their teachers the most important information they need in order to deal with common language problems. Within this framework, the explanations are as complete and accurate as I can make them. However, it is not always helpful or possible in a book of this kind to deal with all the details of a complex structural point; so readers may well find occasional exceptions to some of the grammatical rules given here. Equally, the book does not aim to replace a dictionary. While it gives information about common problems with the use of a number of words, it does not attempt to describe other meanings or uses of the words beside those points that are selected for attention. Nor does it attempt to cover all the vocabulary problems that learners may meet: for this, another complete book would be needed.

This dictionary was originally derived from the Concise Science Dictionary, first published by Oxford University Press in 1984 (fifth edition, retitled Dictionary of Science, 2005). It consisted of all the entries relating to chemistry in this dictionary, including physical chemistry, as well as many of the terms used in biochemistry. Subsequent editions included special feature articles on important topics as well as several chronologies tracing the history of some topics and short biographical entries on the chemists and other scientists who have been responsible for the development of the subject. For this sixth edition the text has been fully revised and some entries have been substantially expanded. In addition over 350 new entries have been added covering all branches of the subject. The coverage of certain fields, in particular biochemistry, forensic chemistry, and chemoinformatics, has been expanded. A further improvement has been the inclusion of about 90 additional chemical structures. An asterisk placed before a word used in an entry indicates that this word can be looked up in the dictionary and will provide further explanation or clarification. However, not every word that appears in the dictionary has an asterisk placed before it. Some entries simply refer the reader to another entry, indicating either that they are synonyms or abbreviations or that they are most conveniently explained in one of the dictionary’s longer articles or features. Synonyms and abbreviations are usually placed within brackets immediately after the headword. Terms that are explained within an entry are highlighted by being printed in boldface type. The more physical aspects of physical chemistry and the physics itself will be found in A Dictionary of Physics, which is a companion volume to this dictionary. A Dictionary of Biology contains a more thorough coverage of the biophysical and biochemical entries from the Dictionary of Science together with the entries relating to biology. SI units are used throughout this book and its companion volumes.

The major reason for undertaking this new approach to teachinglearning Sciences and Mathematics at O level is to improve the academic achievements and interest of learners. The idea of integrating Technology into Sciences and Mathematics at lower secondary education was conceived after realizing that Science and Mathematics teaching at this level hardly generated interest in the learners. In addition, these learners were lacking in practical skills and rarely applied Science and Mathematics to everyday life situations. The National Curriculum Development Centre (NCDC) has developed this new approach of teaching Science and Mathematics by including practical activities that enable learners to come up with products or be able to offer services to the community leading to national sustainable development by generating their own income.