一ひとつ目め

ひ

と

つ

め

Meanings

noun which may take the genitive case particle 'no'

one-eyed

Describes a person, creature, or object having only one eye. Often used in folklore or descriptive contexts.

noun which may take the genitive case particle 'no', noun

Indicates the first item in a sequence or list. Commonly used with nouns like 問題 (question), 理由 (reason), or ステップ (step).

一ひとつ目めの〈事こと〉the first (reason/point/step, etc.)
一ひとつ目めの理り由ゆうは時じ間かんが足たりないことです。
The first reason is that there isn't enough time.
一ひとつ目めは、〜firstly, ... (used when listing points)
一ひとつ目めは健けん康こう、二ふたつ目めは経けい済ざいについてです。
Firstly, health; secondly, the economy.
一ひとつ目めの〈物もの〉a one-eyed (creature/object)
一ひとつ目めのモンスターが物もの語がたりに登とう場じょうする。
A one-eyed monster appears in the story.

最さい初しょN4sense 2
最初 broadly means 'the beginning' or 'at first' in time or sequence, while 一つ目 specifically labels the first item in an enumerated list.
第だい一いちN2sense 2
第一 is a more formal, often written way to say 'first' in a ranking or list, whereas 一つ目 is the everyday spoken equivalent.

一ひとつN5
一つ simply means 'one' (a single item), while 一つ目 means 'the first one' in an ordered sequence or 'one-eyed'.

Compound of 一つ (ひとつ, 'one') and 目 (め, ordinal suffix). The ordinal use is straightforward; the 'one-eyed' sense is a literal reading of the kanji.