The commentary to MN10 even goes as far as taking bhikkhave to include devas.
“Bhikkhave” ti dhammapaṭiggāhakapuggalālapanametaṃ. Bhikkhūti paṭipattisampādakapuggalanidassanametaṃ. Aññepi ca devamanussā paṭipattiṃ sampādentiyeva, seṭṭhattā pana paṭipattiyā bhikkhubhāvadassanato ca, ‘‘bhikkhū’’ti āha. Bhagavato hi anusāsaniṃ sampaṭicchantesu bhikkhu seṭṭho, sabbappakārāya anusāsaniyā bhājanabhāvato, tasmā seṭṭhattā ‘‘bhikkhū’’ti āha. Tasmiṃ gahite pana sesā gahitāva honti rājagamanādīsu rājaggahaṇena sesaparisā viya. Yo ca imaṃ paṭipattiṃ paṭipajjati, so bhikkhu nāma hotīti paṭipattiyā bhikkhubhāvadassanatopi ‘‘bhikkhū’’ti āha. Paṭipannako hi devo vā hotu manusso vā, ‘‘bhikkhū’’ti saṅkhaṃ gacchatiyeva. Yathāha:
‘‘Alaṅkato cepi samaṃ careyya,
Santo danto niyato brahmacārī;
Sabbesu bhūtesu nidhāya daṇḍaṃ,
So brāhmaṇo so samaṇo sa bhikkhū’’ti.
“Bhikkhus”. This is a term for addressing persons who accept the teaching.
Bhikkhu is a term to indicate a person who earnestly endeavors to accomplish the practice of the teaching. Others, devas and humans, too, certainly strive earnestly to accomplish the practice of the teaching, but because of the excellence of the bhikkhu-state by way of practice, the Master said: “Bhikkhu.” For amongst those who accept the teaching of the Buddha, the bhikkhu is the highest owing to fitness for receiving manifold instruction. Further, when that highest kind of person, the bhikkhu, is reckoned, the rest too are reckoned, as in regard to a royal procession and the like, when the king is reckoned, by the reckoning of the king, the retinue is reckoned.
Also the word “bhikkhu” was used by the Buddha to point out the bhikkhu-state through practice of the teaching in this way: “He who practices this practice of the arousing of mindfulness is called a bhikkhu.” He who follows the teaching, be he a deva or a human, is indeed called a bhikkhu. Accordingly it is said:
“Well-dressed one may be, but if one is calm,
Tamed, humble, pure, a man who does no harm
To aught that lives, that one’s a brahman true.
An ascetic and mendicant too.”
(tr. Soma Thera)
So this is the term at its most inclusive.
At the other end of the spectrum we find bhikkhave very narrowly defined as referring only to the bhikkhus who were present on that occasion. Between these two poles the commentaries offer half a dozen or so gradations in different contexts. For example, in the commentary to the fourth bhikkhu pārājika rule the phrase “bad bhikkhus” is said to also include bad bhikkhunīs, sikkhamānās, sāmaṇeras and sāmaṇerīs.