Presumably you're asking for the nominative singular form, this being the form of nouns which is listed in a dictionary.

Word order does matter in Latin. Generally speaking, the earlier a word occurs in a sentence, the more emphatic it is. For example, in 'amor vincit omnia', the emphasis is on 'amor', and it might be rendered 'It is love which conquers all', while 'omnia vincit amor' suggests 'It is everything which love conquers'. This is a complicated but important subject into which I cannot go in depth here, but the following hints may be of help.

In unemphatic speech, the commonest order is subject/indirect object/direct object/verb, alhough it is by no means always true, as is often asserted, that the verb usually comes last in a Latin sentence, as the tag from Ovid which you quote indicates. Adjectives and appositive nouns usually follow the nouns which they modify unless emphatic, in which case they precede it, but the commonest adjectives (such as bonus, malus, etc.) and adjectives indicating quantity (magnus, multus, pauci, etc.) normally precede even when not emphatic, as do demonstrative, relative, and interrogative adjectives. Possessive adjectives usually follow. Cardinal numerals (unus, duo, etc.) precede, ordinal numerals (primus, secundus) follow. When the genitive is an equivilent of an adjective or dependemnt on its noun it follows, but when indicating possession it often precedes. Adverbs and phrases used as adverbs usually precede the verb. A complementary infinitive generally precedes the verb which it complements, as does a subject accusative.

These are just a very few observations. The best method, however, of acquiring a sense of the natural word order in Latin is carefully to observe the usage of good writers because most of the so-called rules are very frequently abandoned. For example, although conjunctions usually fall at the beginning of a sentence or clause, a number of them (as 'autem', 'enim', 'quidem', quoque', 'vero', and some others) always follow one or more words. Even preopositions occasionally follow rather than precede their nouns; one which always follows them is 'versus'.



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Note added at 1 hr 7 mins (2005-10-07 23:33:13 GMT) Post-grading
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As Maria notes, 'fidelitas' is indeed synonymous with 'fides' in this sense.