mjhjmtu

In Devi Suktam, word (sarvabhūteṣu) is repeated for different manifestations of Devi.
I am quite sure with Sarva(सर्व) means all, but word Bhoota (भूत) just confused me a lot.

Bhoota is quite commonly used for Past in context of past, present, future.

Also somewhere I read it is used living beings.

Also Hindi meaning modernly used for spirits of person after death.

Also in Pancha Bhoota (पञ्चभूत pañcabhūta) or Pancha Maha-Bhoota (पञ्चमहाभूत pañcamahābhūta) context, it is used for five prime elements of nature (Air, Water, Fire, Space, Earth). So here Bhoota means elements.

What is actual meaning of this word (Bhoota) in context of Devi Suktam?

Yes, the sanskrit word Bhuta can have different meanings e.g. 1. For addressing happened in past, 2. For Pancha Mahabhuta (five elements - Agni, Vayu, Jala, Prithivi and Aakash) and 3. For living beings. More accurate translation would be "becoming" or manifasting.

Here it's used to address living beings. According to Sanskrit Dictionary:

bhūta भूत

Definition: n. (see above) that which is or exists, any living being (divine, human, animal, and even vegetable), the world (in these senses also m.) etc.

This meaning or interpretation is nicely supported in the famous context of Bhagavad Gita 15.7

ममैवांशो जीवलोके जीवभूतः सनातनः।

मनःषष्ठानीन्द्रियाणि प्रकृतिस्थानि कर्षति।।15.7।।

15.7 It is verily a part of Mine which, becoming the eternal individual soul in the region of living beings, draws (to itself) the organs which have the mind as their sixth, and which abide in Nature.

You can refer सार्थश्लोकसङ्ग्रह (Collection of Commonly Recited Shlokas with Meanings) from Sanskrit Documents where word-to-word translation is provided:

या देवी सर्वभूतेषु मातृरूपेण संस्थिता ।

या देवी सर्वभूतेषु शक्तिरूपेण संस्थिता ।

या देवी सर्वभूतेषु शान्तिरूपेण संस्थिता ।

नमस्तस्यै नमस्तस्यै नमस्तस्यै नमो नमः ।

ॐ अम्बायै नमः ॥ ॥

Adorations to the Divine Mother! Again and again adorations unto that Devi (Goddess) who manifests in all living beings as the Mother. Adorations to Her! Again and again adorations unto that Devi (Goddess) who manifests in all living beings as Energy. Adorations to Her! Again and again adorations unto that Devi (Goddess) who manifests in all living beings as Peace. Adorations to Her!.

या = She who;

देवी = goddess;
सर्वभूतेषु = among all the living beings;

शान्तिरूपेण = in the form of peace;

संस्थिता = well-positioned; standing well;

नमस्तस्यै = salutations unto thee;

नमस्तस्यै = salutations unto thee;

नमस्तस्यै = salutations unto thee;

नमो = bowing; salute;

नमः = bowing; salutation;

ॐ = same as 'OM' i.e. the praNava or 'o.nkAra' mantra; अम्बायै = to the goddess or mother; नमः = bowing; salutation;

By the way it would be fine if we take the meaning of Bhuta as PanchaBhuta + Jiva (to consider non-living or insentient being made up of Pancha Mahabhuta and living or sentient being) as according to Vedanta, the supreme-self (परमात्मा) is the inner self of Jiva and Jagat as well, however the qualities like शक्तिरूपेण, श्रद्धारुपेण etc. are not manifested in insentient beings. So, it would be appropriate to consider living beings in which the supreme-self (here various forms of Devi) dwells.