Gesenius' Hebrew Grammar/98. Numerals. (b) Ordinal Numbers
a The ordinal numbers from 2 to 10 are formed from the corresponding cardinals by adding the termination ־ִי (§ 86 h), before which another ־ִי also is generally inserted between the second and third radicals. They are as follows: שֵׁנִי second, שְׁלִישִׁי, רְבִיעִי (like רֶ֫בַע, רֹ֫בַע, רִבֵּעִים, without the prosthetic א, which appears in אַרְבַּע, &c.), חֲמִישִׁי or חֲמִשִׁי (which, according to Strack, is always to be read for חֲמִשִּׁי), שִׁשִּׁי, שְׁבִיעִי, שְׁמִינִי, תְּשִׁיעִי, עֲשִׂירִי. The ordinal first is expressed by רִאשׁוֹן (cf. § 27 w), from רֹאשׁ head, beginning, with the termination וֹן (§ 86 f). On the use of אֶחָד as an ordinal in numbering the days of the month, cf. § 134 p; in such cases as Gn 1, 2, the meaning of first is derived solely from the context.
b The feminine forms have the termination ־ִית, more rarely (and only in the case of 3 and 10) ־ִיָּה. They are employed also to express fractions, e.g. חֲמִשִׁית fifth or fifth part, עֲשִׂירִית and עֲשִֽׂירִיָּה tenth part. Side by side with these, in the same sense, there are also forms like רֹ֫בֵע and רֶֹ֫בַע a quarter, חֹ֫מֶשׁ a fifth part, and with the afformative וֹן, עִשָּׂרוֹן (plur. עֶשְׂרוֹנִים) a tenth part; these are to be regarded as abstracts, and are denominatives from the cardinal numbers. Cf. finally שָׁבוּעַ ἑβδομάς, a week; עָשׂוֹר a decade (of days), and also the tenth day.
On the expression of the other relations of number, for which the Hebrew has no special forms, see the Syntax, § 134 q and r.